The invention relates, according to an aspect thereof, to a method for evaluating and/or calibrating a fuel injector in a fuel burner in an exhaust gas treatment system for an internal, combustion engine.
Modern diesel combustion engines are equipped with a diesel particle filter (DPF) in the exhaust system. Soot from engine's combustion is trapped in the DPF. The soot is periodically cleaned out with oxidation (regeneration), whereas the exhaust temperature before the DPF is one key parameter. The temperature is often controlled by a burner. In order to minimize regeneration time, a gas temperature of approximately 600° C. is typically desired before the DPF. Normally, temperature needs to be controlled with a maximum temperature error of a few percent.
The fuel to the burner is diesel, controlled by a fuel injector. The oxygen to burn fuel in burner comes from rest oxygen from engine combustion. In case of high power burners, added oxygen is needed in order to burn sufficient amount of fuel. Methods to add this oxygen can be auxiliary air pumps or compressors.
For high performance burners, the burner will at some conditions run close to operating limits with respect to flame/combustion stability for the given design of the burner. Typical operations close to functional limits of burner are (A) high exhaust flow where very high burner power is required and (B) low exhaust flow where very low power of burner is needed. For burners with auxiliary air pumps or compressors connected to engine by fixed ratio to engine speed (gears or similar) two further points close to burner limitation need to be added: (C) low engine revs with high burner power and (D) high engine revs with low burner power.
The points described above, where the burner need to be run close to operating limits are characterized by either of following:
(A) Limitation of combustion time in burners combustion chamber
(B) Flame size/stability limitation
(C) Limitation of oxygen
(D) Flame size/stability limitation
Consequences of limitations may be increased emissions or prolonged regeneration time.
Due to above physical limitation of burners, it is very important to have correct fuel to the burner. A correct fuel amount to the burner maximizes burner operation area and functionality. Incorrect fuel amount to the burner increases above limitations.
According to the above, a method is needed, which allows a reliable evaluation and/or calibration of the burner fuel injector, such that the fuel injector delivers a reliable and desirable amount of fuel during at least two, preferably three or more, more preferred all, operating conditions of the fuel injector.
It is desirable to suggest a method for evaluation of a fuel injector in an exhaust gas treatment system.
As such, the present disclosure relates to a method for evaluating the fuel injection accuracy of at least one fuel injector in an exhaust gas treatment system for an internal combustion engine, wherein the at least one fuel injector is mounted upstream of a diesel particle filter, the method comprising:
injecting fuel by the at least one fuel injector with a first pulse width, registering a first temperature of an exhaust gas downstream of the at least one fuel injector,
injecting fuel by the at least one fuel injector with a second pulse width, the second pulse width being different from the first pulse width, whereby the at least one fuel injector is controlled in order to inject substantially the same amount of fuel during a time range as the amount of fuel that was injected using the first pulse width during a corresponding time range,
registering a second temperature of an exhaust gas downstream of the at least one fuel injector, and
determining a temperature difference between the first temperature and the second temperature.
As used herein, the expression “pulse width” includes a limited time interval during which fuel is injected from the at least one fuel injector. As such, when fuel is injected with a pulse width, substantially no fuel is injected between two subsequent pulses.
Preferably, the above method is performed during a constant temperature of a burner of which the at least one fuel injector forms a part. The fuel burner assumes a constant temperature when the temperature of the exhaust gases from the engine have a constant temperature, this occurs for example during idle speed of the engine or during an engine braking situation or any situation when the engine is driven in a steady state.
Preferably, the method may further comprise a step of calculating a correction factor for the at least one fuel injector dependent of the temperature difference.
Based upon the above discussed temperature difference, it is possible to assess whether the at least one fuel injector has an appropriate fuel injection accuracy or not. Purely by way of example, if the absolute value of the temperature difference is above a predetermined temperature threshold value, this may be an indication that the at least one fuel injector needs to be replaced and/or adjusted.
As another non-limiting example, the above discussed temperature difference may be used as an input to a calibration method wherein the characteristics of the at least one fuel injector, for instance as regards the fuel pressure and/or fuel flow rate, are calibrated.
The method of the present disclosure is based on the findings that for fuel injectors having a short pulse width, the spread between a desired and an actual amount of injected fuel is generally low for all fuel injectors. However with an increasing pulse width, the deviation of the actual injected amount of fuel and the desired amount of fuel is increasing. It is found that this deviation increases essentially linear with increased pulse width, whereby it is beneficial to perform an evaluation, and possibly also a calibration, of a fuel injector when it is operated with a long pulse width.
The above method further uses the long reaction time of the sensing means in the exhaust system, which smoothens fast variations in the temperature. That is, because the fuel is injected in pulses and not continuously, the actual temperature will be oscillating, however because of the relative long reaction time the measured temperature will be constant during a steady state operation of the fuel burner.
Optionally, the evaluation method is performed during an idle speed of the combustion engine.
Optionally, the second pulse width, is longer than the first pulse width.
Optionally, the second pulse width is at least five times greater, preferably eight times greater, than the first pulse width.
Optionally, the method further comprises, after fuel, has been injected with the second pulse width:                injecting fuel by the at least one fuel injector with the first pulse width,        registering a third temperature of an exhaust gas downstream of the at least one fuel injector, and        determining a second temperature difference between the second temperature and the third temperature.        
Optionally, the method is performed at start up, preferably every start up, of the vehicle.
Optionally, the method is performed after service, preferably after every service, of the vehicle.
A second aspect of the present disclosure relates to a method for calibrating at least one fuel injector for a fuel burner in an exhaust gas treatment system for an internal combustion engine, the method comprising:                determining a temperature difference using an evaluation method according to the first aspect of the present disclosure, and        adjusting at least one fuel injection characteristic of the at least one fuel injector in response to the temperature difference.        
Purely by way of example, the at least one fuel injection characteristic may comprise at least one of the following characteristics: the fuel pressure of the fuel delivered to die at least one fuel injector or the fuel flow rate of the fuel leaving the at least one fuel injector. Purely by way of example, the fuel pressure may be controlled by a pump in communication with the at least one fuel injector. As such, the fuel pressure may be adjusted by adjusting the pump actuation.
Moreover, and again purely by way of example, the magnitude of the fuel flow rate may be controlled by the opening degree of one or more valves. Purely by way of example, the one or more valves may be located in the at least fuel injector as such or in one or more conduits connecting a fuel pump with the at least one fuel injector. As such, the fuel flow rate may be adjusted by adjusting the opening degree of the one or more valves.
Optionally, the method according to the second aspect further comprises:                adjusting the at least one fuel injection characteristic associated with the first pulse width or the second pulse width in response to the temperature difference.        
Optionally, the method according to the second aspect further comprises:                adjusting the at least one fuel injection characteristic associated with the widest one of the first pulse width and the the second pulse width in response to the temperature difference.        
It is desirable to suggest a method for calibration of a fuel injector in an exhaust gas treatment system, such that it during all conditions delivers a desired amount of fuel.
The method according to the third aspect of the present disclosure is based on the findings that for fuel injectors having a short pulse width, the spread between a desired and an actual amount of injected fuel is low for all fuel injectors. However with an increasing pulse width, the deviation of the actual injected amount of fuel and the desired amount of fuel is increasing. It is found that this deviation increases essentially linear with, increased pulse width, whereby it is beneficial to perform a calibration of a fuel injector when it operated with a long pulse width.
The third aspect of the present disclosure further rises the long reaction time of the sensing means in the exhaust system, which smoothers fast variations in the temperature. That is, because the fuel is injected in pulses and not continuously, the actual temperature win be oscillating, however because of the relative long reaction time the measured temperature will be constant during a steady state operation of the fuel burner.
A method of calibration of at least one fuel injector of a fuel burner in an exhaust gas treatment system for an internal combustion engine is therefore, according to the third aspect of the present disclosure, suggested. The method according to the third aspect of the present disclosure is adapted for an exhaust gas system having said fuel burner mounted upstream of a diesel particle filter (DPF). The method of calibration is performed during a constant temperature of the burner. The fuel burner becomes a constant temperature when the temperature of the exhaust gases from the engine have a constant temperature, this occurs for example during idle speed of the engine or during an engine braking situation or any situation when the engine is driven in a steady state.
The method, according to the third aspect of the present disclosure, is started when a first steady temperature Is registered in the fuel burner, wherein said at least one fuel injector is operated with a first pulse width, and thereby aiming to inject a first amount of fuel during a specific time period. A first temperature of an exhaust gas is registered directly downstream of the fuel burner. After this first temperature is registered, the pulse width of the fuel injector is changed into a second pulse width, which is different from the first pulse width, whereby the at least one fuel injector still aims to inject the same amount of fuel during the same time period.
If the fuel injector is correctly calibrated, a change in pulse width of the fuel injector will, over a predetermined time, not influence the total amount of injected fuel in the fuel burner, and therefore also not result in any change in temperature in the fuel burner. However an erroneous calibrated fuel injector will, with a changed pulse width, inject more or less fuel in the fuel burner during the same predetermined time, wherein the temperature in the fuel burner will rise or fall respectively. Since the exhaust gas from the engine has the same temperature during the whole calibrating process (performed in a steady state of the vehicle), any difference in temperature in the exhaust gas derives from a change in the amount of fuel that has been burned in the fuel burner.
Hence, after the pulse width of the fuel injector has been changed and a steady state of the system is has been achieved, then the second temperature of the exhaust gas directly downstream of the fuel burner is registered. The second temperature is compared with the first temperature, wherein a temperature difference between the first and the second temperatures is calculated. The temperature difference is a measure of the difference in injected fuel during said specific time period, and if the fuel injector is correctly calibrated this difference is equal to zero.
Thereby, since the spread of the injected fuel is linear and trough the temperature difference a correction factor for the at least one fuel injector can be calculated dependent of the temperature difference between the short and long pulse width. The correction factor corrects the difference in the amount of fuel that is injected with different pulse width, such that during a reference time, the same amount of fuel, is injected in the fuel burner independently of the pulse width of the fuel injector.
The method according to the third aspect of the present disclosure is preferably performed during an idle speed of the engine, when the engine has reached a steady state operating temperature.
As short pulse width is preferred, the pulse width of the at least one fuel injector is changed back to the first pulse width after the second temperature has been registered. A short pulse width assures a steady flow of fuel.
The method according to the third aspect of the present disclosure further comprises the step of changing a correction factor for the fuel injector. The calculated correction factor assures that the fuel injector always injects the correct amount of fuel. The correction factor compensates the error that occurs when the pulse width is increased and thereby assures that the amount of fuel injected during a specific period of time is independent of the pulse width.
A preferred first pulse width is 1/10 and a preferred second pulse width is 9/10, i.e. the short pulse width is nine times shorter than the long pulse width, whereby nine fuel injections with the short pulse width is supposed to be equal one fuel injection of the long pulse width. For example, with the short pulse width—1/10—, is during one time unit, nine fuel injections made and with the long pulse width—9/10—, is one fuel injection made during the same time unit, wherein with a correct calibrated fuel injector this results in the same amount of injected fuel.
The method according to the third aspect of the present disclosure can be performed at any suitable situation as long as the steady temperature condition is fulfilled, whereby normally is a new calibration of the fuel injector not needed continuously, therefore it is suggested that the method is performed at every start up of the vehicle or more preferably after a service of the vehicle. Once the fuel injector is calibrated, it normally has a stable functionality, whereby a new calibration must just be made when the fuel injector has been changed.
It should be noted that features of the third aspect of the present disclosure may be incorporated in the method according to the first aspect of the present disclosure and/or the method according to the second aspect of the present disclosure.